I want to add to the link to my post(Strategy to Assess and Control Nitrosamine Formation in API during Storage: A Sitagliptin Case Study). As it may be rare case, residual secondary amine(LT 100ppb) in Sitagliptin Hydrochloride Monohydrate caused nitrosamine formation in storage due to NOx gass in the air.
Besides, I classified 161 Nitrosamines in EMA Appendix 1 by structure, 5% was from Tertiary amides.
Nitrosamines with CPCA cat.1 and 2 derived from amides may be concerning in some cases.